The goal of these studies is to increase understanding of the diagnostic, therapeutic and pathogenicity aspects of parasitic infections. Reliable serodiagnostic assays have been developed for filariasis (detection of circulating antigen), strongyloides (detection of IgG antibodies) and schistosomiasis (detection of IgG and IgM antibodies). Under development are diagnostic assays for strongyloides (skin test), cryptosporidia (serum antibody) and schistofibrotic liver complication of schistosomiasis (by ultrasonography). Therapeutic studies indicate that while heat treatment is effective for lesions of patients with disseminated cutaneous leishmaniasis (DCL) of the Americas, it is ineffective in Ethiopian DCL. Long-term studies of diethylcarbamazine (DEC) used prophylactically for loiasis are underway in Africa. The pathology of parasitic infections results from both the patients' immune responses to the parasite and the pathogenic potential of the parasite itself. For helminth infections (filariasis, schistosomiasis, onchocerciasis, loiasis, strongyloidiasis) cellular and humoral (especially IgE and the subclasses of IgG) immune responses and their specific regulatory mechanisms have been characterized. Additionally, bronchial lavage in patients with tropical eosinophilia has indicated the presence of an eosinophil-macrophage alveolitis; the locally destructive inflammatory mediators are being characterized. Studies of the violent side effects of treatment with DEC in patients with onchocerciasis indicate important roles for complement and immediate hypersensitivity immune mechanisms in initiating these reactions. Work on pathogenicity in protozoal infections (giardiasis, leishmaniasis) has focused primarily on strain differences among the parasites and their roles in determining the character of the pathology and the clinical response of these patients to treatment. Additionally, the importance and mechanisms of immunologic anergy in patients with DCL are under study.